Semiconductor device and production process thereof

ABSTRACT

A semiconductor device having a pad for electrical connection provided on a semiconductor substrate, a first insulating film with which a surface of the semiconductor substrate is coated and having an opening to which the pad is exposed, a conductive film joined to the pad on a bottom surface of the opening of the first insulating film and extending to a surface of the first insulating film outside the opening, a second insulating film with which the conductive film is coated and having an opening to which a part of the conductive film is exposed, and a connecting member arranged so as to be joined to the conductive film inside the opening of the second insulating film.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a semiconductor device having aconductive film connected to a pad on a semiconductor substrate and aproduction process thereof.

[0003] 2. Description of Related Art

[0004] In a chip-on-chip structure in which active surfaces of a pair ofsemiconductor chips are overlapped with each other, and in a flip chipbonding structure in which a semiconductor chip is joined to a wiringboard with its active surface opposed to the wiring board, a projectionfor electrical connection called a bump is provided on the activesurface of the semiconductor chip. FIG. 3 illustrates construction inthe vicinity of a surface of the semiconductor chip.

[0005] A pad 52 to which a part of an external wiring is exposed isprovided on an active surface 51 a of a semiconductor substrate 51. Theactive surface 51 a of the semiconductor substrate 51 is covered with apolyimide film 54 having an opening 53 to which the pad 52 is exposed. Abump 55 is arranged on the pad 52 in the opening 53. The bump 55projects from a surface of the polyimide film 54.

[0006] The bump 55 is formed by electroless plating, for example. In theelectroless plating, a metal film having good adhesive properties cannotbe formed on the surface of the polyimide film 54. By merely growing athick film of a conductor such as gold or copper on the pad 52 insidethe opening 53, therefore, the bump 55 is formed.

[0007] However, it takes long to form the thick film by the electrolessplating. Accordingly, it takes significantly long to fill in the opening53 formed in the polyimide film 54 and form the bump 55 projecting fromthe surface of the polyimide film 54. Therefore, time required toproduce the semiconductor chip is long.

SUMMARY OF THE INVENTION

[0008] An object of the present invention is to provide a semiconductordevice, having a connecting member, whose productivity can be improvedand a production process thereof.

[0009] Another object of the present invention is to provide a processof producing a semiconductor device, in which a low-resistive conductivefilm having good adhesive properties can be formed on a surface of aninsulating film on a semiconductor substrate in a short time.

[0010] A semiconductor device according to the present inventioncomprises a pad for electrical connection provided on a semiconductorsubstrate; a first insulating film with which a surface of thesemiconductor substrate is coated and having an opening to which the padis exposed; a conductive film joined to the pad on a bottom surface ofthe opening of the first insulating film and extending to a surface ofthe first insulating film outside the opening; a second insulating filmwith which the conductive film is coated and having an opening to whicha part of the conductive film is exposed; and a connecting memberarranged so as to be joined to the conductive film inside the opening ofthe second insulating film.

[0011] The semiconductor device can be produced by a production processcomprising the steps of coating a surface of a semiconductor substrate,provided with a pad for electrical connection, with a first insulatingfilm having an opening to which the pad is exposed; modifying a surfaceof the first insulating film and an inner wall surface of the opening;forming by an ion-exchange reaction a thin conductive film with whichthe surface of the first insulating film, the inner wall surface of theopening, and a surface of the pad exposed on a bottom surface of theopening is coated; thickening the thin conductive film by electroplatingwith power being fed using the thin conductive film; forming a secondinsulating film with which the thickened conductive film is coated andhaving an opening to which a part of the conductive film is exposed; andforming a connecting member joined to the thickened conductive filminside the opening of the second insulating film.

[0012] According to the process, by modifying the surface of the firstinsulating film and the inner wall surface of the opening formed in thefirst insulating film, the thin conductive film having good adhesiveproperties can be formed by utilizing the ion-exchange reaction on themodified surfaces. Power can be fed using the thin conductive film,thereby making it possible to thicken the thin conductive film by theelectroplating. The conductive film can be thickened in a short time bythe electroplating. As a result, the thickened conductive film havinggood adhesive properties can be quickly formed on the first insulatingfilm. After the thickened conductive film is then coated with the secondinsulating film, and the opening is formed in the second insulting film,the connecting member joined to the thickened conductive film may beformed in the opening.

[0013] The surface modification processing for the first insulating filmmay be processing for introducing a cation exchange group into thesurface of the first insulating film. The surface of the firstinsulating film which has been subjected to the surface modificationprocessing is brought into contact with a solution containing ions of ametal material to compose the conductive film, thereby making itpossible to produce the ion-exchange reaction. By the ion-exchangereaction, the metal ions are replaced with the cation exchange group,and the cation exchange group is sucked by the surface of the firstinsulating film.

[0014] The connecting member may be a bump for connection to anothersolid device (e.g., another semiconductor chip or wiring board).

[0015] The connecting member may be another conductive film joined tothe conductive film on the bottom surface of the opening in the secondinsulating film and extending to the surface of the second insulatingfilm. In this case, a so-called multi-layered wiring structure isconstituted by a two-layer conductive film insulated by the secondinsulating film.

[0016] The first insulating film may be composed of polyimide resin. Inthis case, the modification processing for the surface of the firstinsulating film and the inner wall surface of the opening formed in thefirst insulating film may be processing for cleaving an imide ring ofthe polyimide resin using a potassium hydroxide solution, for example,and introducing a carboxyl group serving as the cation exchange groupinto the surface of the first insulating film. Thereafter, the firstinsulating film is immersed in the solution containing the ions of themetal material composing the connecting member, thereby making itpossible to produce the ion-exchange reaction on the surface of thefirst insulating film and form the connecting member composed of themetal material on the surface of the first insulating film, the innerwall surface of the opening, and the surface of the pad.

[0017] As a material for the first insulating film, epoxy resin, forexample, can be used in addition to the polyimide resin. In this case,the surface modification processing for the first insulating film may beprocessing for immersing the first insulating film in a sulfuric acidsolution to introduce a sulfo group serving as the cation exchange groupinto its surface. When an epoxy resin film which has been thus subjectedto the surface modification processing is immersed in the solutioncontaining the metal ions to produce the ion-exchange reaction, themetal ions are sucked by the surface of the first insulating film.

[0018] As a material for the first insulating film, resin including animide bond or an acido bond or including both an imide bond and an acidobond can be used in addition thereto.

[0019] As the second insulating film, the resin including an imide bondor an acido bond or both an imide bond and an acido bond can be used, inaddition to the polyimide resin or the epoxy resin, as a materialcomposing the second insulating film, similarly to the first insulatingfilm. Particularly when a multi-layered wiring structure is formed usinga pair of conductive films insulated by the second insulating film, itis preferable that the surface of the second insulating film and theinner wall surface of the opening are subjected to the above-mentionedsurface modification processing using the polyimide resin or the epoxyresin as the material composing the second insulating film.

[0020] A process according to another mode of the present inventioncomprises the steps of forming an insulating film on a semiconductorsubstrate; modifying a surface of the insulating film; forming a thinconductive film by an ion-exchange reaction on the modified surface ofthe insulating film; and thickening the thin conductive film byelectroplating for feeding power using the thin conductive film.

[0021] According to the process, the conductive film having goodadhesive properties can be formed on the surface of the insulating filmby performing the ion-exchange reaction subsequently to the surfacemodification processing for the insulating film. The thin conductivefilm is thickened by the electroplating, thereby making it possible toform a low-resistive conductive film having good adhesive properties ina short time on the insulating film. This can contribute to animprovement in the productivity of the semiconductor device.

[0022] The foregoing and other objects, features, aspects and advantagesof the present invention will become more apparent from the followingdetailed description of the present invention when taken in conjunctionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023]FIGS. 1A to 1E are cross-sectional views showing the steps of aprocess of producing a semiconductor device according to a firstembodiment of the present invention;

[0024]FIG. 2 is an illustrative sectional view for explaining a processof producing a semiconductor device according to a second embodiment ofthe present invention; and

[0025]FIG. 3 is a cross-sectional view for explaining the prior art forforming a bump on an active surface of a semiconductor substrate.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026]FIGS. 1A to 1E are cross-sectional views showing the steps of aprocess of producing a semiconductor device according to a firstembodiment of the present invention. A plurality of device formingregions corresponding to a plurality of semiconductor chips are providedon a surface of a semiconductor wafer W (a semiconductor substrate), andthe plurality of device forming regions are separated by a scribe lineregion L. The scribe line region L is a region along a cutting line in acase where the semiconductor chips are cut out of the wafer W by adicing saw.

[0027] In the device forming region corresponding to each of thesemiconductor chips, a pad P for electrical connection to another soliddevice (a semiconductor chip or a wiring board, etc.) is provided on anactive surface Wa. The pad P is exposed from an opening 11 a formed in afirst polyimide film 11 (a first insulating film) with which the activesurface Wa is coated. The pad P is an exposed part of an internal wiringelectrically connected to an internal circuit, comprising functionaldevices such as transistors and resistors, formed on the active surface.

[0028] A thin conductive film 21 a is formed, as shown in FIG. 1B, froma state shown in FIG. 1A where the first polyimide film 11 is formed onthe active surface Wa. A process reported in “Basic study for DirectMetallization Using Surface Modification of Polyimide and Epoxy Resin”(by Nawafune et. al., Journal of JIEP (Japan Institute of ElectronicsPackaging), Vol. 2, No. 5 (1999), pp 390-393), “Production of Co/PtMulti-layered Film Utilizing Surface Modification of Polyimide Resin andMagnetic Properties” (by Tamura et. al., the substance of the 99-thConference of The Surface Finishing Society of Japan (1999), pp 35-36) ,etc. can be applied to the formation of the thin conductive film 21 a.

[0029] Specifically, the surface of the first polyimide film 11 and theinner wall surface of the opening 11 a are subjected to surfacemodification processing. The surface modification processing isperformed specifically by immersing in a potassium hydroxide solutionthe semiconductor wafer W in the state shown in FIG. 1A where the firstpolyimide film 11 is formed, cleaving an imide ring in a surface layerportion of the first polyimide film 11, and introducing a carboxyl groupinto the surface of the first polyimide film 11.

[0030] The thin conductive film 21 a can be thus formed with goodadhesive properties by an ion-exchange reaction on the surface of thefirst polyimide film 11 which has been subjected to the surfacemodification processing. The ion-exchange reaction can be performed byimmersing in a solution containing metal ions the semiconductor wafer Win a state where the first polyimide film 11 has been subjected to thesurface modification processing. If the semiconductor wafer W isimmersed in a copper sulfate solution, for example, a copper thin filmserving as the thin conductive film 21 a can be provided on the surfaceof the first polyimide film 11, the inner wall surface of the opening 11a, and the surface of the pad P.

[0031] After the thin conductive film 21 a is thus formed on the surfaceof the first polyimide film 11, a thick conductive film 21 is formed, asshown in FIG. 1C, by electroplating for feeding power using the thinconductive film 21 a. That is, the conductive film 21 which is madelow-resistive is formed on the surface of the first polyimide film 11 bythickening the thin conductive film 21 a using the electroplating. Thepower can be fed at the time of the electroplating by connecting thethin conductive film 21 a in the scribe line region L to an electrode.

[0032] Since the thin conductive film 21 a can be thickened in a shorttime by the electroplating, the formation of the conductive film 21formed through the formation of the thin conductive film 21 a by theion-exchange reaction and the thickening thereof can be achieved in ashort-time step.

[0033] As shown in FIG. 1D, the pattern of a resist film 15 is formed onthe surface of the first polyimide film 11. Prior to forming the resistfilm 15, an insulating film 17 may be buried in a depression 25 formedin a portion, corresponding to the opening 11 a, in the thickenedconductive film 21 a.

[0034] The conductive film 21 is then patterned by etching using theresist film 15 as a mask. Thereafter, as shown in FIG. 1E, the resistfilm 15 is stripped, and a second polyimide film 12 (a second insulatingfilm) is formed such that a surface of the conductive film 21 and thesurface of the first polyimide film 11 exposed by etching away anunnecessary portion of the conductive film 21 are coated therewith. Anopening 12 a is formed at a position, avoiding the opening 11 a in thefirst polyimide film 11, in the second polyimide film 12. A bump B isprovided in the opening 12 a.

[0035] If an opening 11 b is formed in the first polyimide film 11 inthe scribe line region L, the bump B can be quickly formed by theelectroplating performed by feeding power from the conductive film 21exposed from the opening 11 b. The bump B is formed in the shape of athick film filling in the opening 12 a and projecting from a surface ofthe second polyimide film 12 in a quick step by the electroplating.

[0036] Thereafter, the wafer W is cut by a dicing saw along the scribeline region L, thereby obtaining respective pieces of semiconductorchips.

[0037] As described in the foregoing, according to the presentembodiment, the thin conductive film 21 a is formed by the surfacemodification processing for the first polyimide film 11 and theion-exchange reaction for the surface of the first polyimide film 11after the surface modification processing. The conductive film 21 whichis made low-resistive can be provided on the first polyimide film 11 bythickening the thin conductive film 21 a. So long time is not requiredto form the thin conductive film 21 a by the ion-exchange reaction.Further, the thin conductive film 21 a can be quickly thickened by theelectroplating. Consequently, the productivity of the semiconductor chipcan be improved.

[0038] The semiconductor chip produced in accordance with the processaccording to the present embodiment has the bump B serving as aconnecting member to another solid device at a position shifted from theopening 11 a formed in the first polyimide film 11, as shown in FIG. 1E.As a result, the first polyimide film 11 is interposed between the bumpB and the active surface Wa of the wafer W serving as the semiconductorsubstrate. Such a structure is advantageous that when it is joined toanother solid device, pressure received by the bump B is not directlyexerted on the semiconductor substrate (the wafer W). Further, the firstand second polyimide films 11 and 12 are interposed between the othersolid device and the active surface Wa of the semiconductor chip.Consequently, the difference in the coefficient of thermal expansionbetween the solid device and the semiconductor chip can besatisfactorily absorbed. Therefore, stress caused by the difference inthe coefficient of the thermal expansion can be effectively preventedfrom being exerted on the semiconductor substrate.

[0039]FIG. 2 is an illustrative sectional view for explaining a processof producing a semiconductor device according to a second embodiment ofthe present invention. In FIG. 2, portions corresponding to the portionsshown in FIGS. 1A to 1E, described above, are assigned the samereference numerals as those shown in FIGS. 1A to 1E.

[0040] In the second embodiment, a multi-layered wiring structure isformed on a wafer W. That is, a second conductive film 22 is formed on asurface of a second polyimide film 12. The second conductive film 22 isjoined to a first conductive film 21 at the bottom of an opening 12 aformed in the second polyimide film 12. The second conductive film 22rises along an inner wall surface of the opening 12 a, and furtherextends to the surface of the second polyimide film 12.

[0041] The second conductive film 22 can be formed by the same processas that forming the first conductive film 21. That is, surfacemodification processing for the second polyimide film 12 is performed inthe same manner as surface modification processing for a first polyimidefilm 11. A thin conductive film is formed by utilizing an ion-exchangereaction on the surface of the second polyimide film 12 which has beenthus subjected to the surface modification processing. The thinconductive film is brought into contact with the first conductive film21 in the opening 12 a. Accordingly, power is fed from the firstconductive film 21 to thicken the thin conductive film formed on thesecond polyimide film 12 by electroplating, thereby making it possibleto provide the thickened conductive film 22. The second conductive film22 has a depression 26 at a position corresponding to the opening 12 a.However, the depression 26 is filled with an insulating material 27, asrequired.

[0042] The second conductive film 22 is patterned, as required.Thereafter, an insulating film 13 (e.g., a polyimide film) is formed soas to cover the second conductive film 22 and the surface of the secondpolyimide film 12 exposed by patterning the second conductive film 22.An opening 13 a is formed at a position, avoiding the opening 12 a, inthe insulating film 13. A bump B is buried in the opening 13 a. If anopening 13 b is formed in the insulating film 13 in a scribe line regionL, the bump B can be formed by the electroplating performed by powerfeeding through the first conductive film 21 and the second conductivefilm 22 in the scribe line region L.

[0043] As described in the foregoing, according to the secondembodiment, a wiring having a two-layer structure can be provided on thewafer W by forming the thin conductive film using the surfacemodification processing and the ion-exchange reaction for the polyimidefilms and thickening the thin conductive film using the electroplating.

[0044] Although description has been made of the two embodiments of thepresent invention, the present invention can be embodied in anothermode. Although in the above-mentioned first and second embodiments,polyimide resin is used as a material for the first and secondinsulating films, for example, epoxy resin can be also used. In thiscase, it is preferable that surface modification processing isprocessing for immersing in a sulfuric acid solution a wafer having afilm composed of epoxy resin formed therein to introduce a sulfo groupinto a surface of the epoxy resin film. The sulfo group is replaced withmetal ions by ion-exchange resin, thereby making it possible to form athin conductive film on the surface of the epoxy resin film.

[0045] Although in the above-mentioned first and second embodiments, thedepressions 25 and 26 in the first and second conductive films 21 and 22are respectively filled with the insulating materials 17 and 27, thefilling with the insulating materials 17 and 27 may be omitted.

[0046] A metal material having conductive properties, for example,cobalt or nickel can be used in addition to copper as a material for theconductive films 21 and 22. The same is true for a material for the bumpB. However, the same material as that for the conductive films 21 and 22is preferably used as the material for the bump B.

[0047] Although in the above-mentioned second embodiment, descriptionhas been made of an example in which the wiring having a two-layerstructure is provided on the active surface Wa of the wafer W, amulti-layered wiring structure comprising three or more layers can bealso formed in the same manner.

[0048] Although in the above-mentioned first and second embodiments,description has been made of an example in which both the first andsecond insulating films are composed of polyimide resin, they may becomposed of epoxy resin, as described above, and they may berespectively composed of different insulating resin materials.

[0049] Although the present invention has been described and illustratedin detail, it is clearly understood that the same is by way ofillustration and example only and is not to be taken by way oflimitation, the spirit and scope of the present invention being limitedonly by the terms of the appended claims.

[0050] The application corresponds to Japanese Patent Application SerialNo. 2000-89174 filed with the Japanese Patent Office on Mar. 28, 2000,the disclosure of which is incorporated herein by reference.

What is claimed is:
 1. A semiconductor device comprising: a pad forelectrical connection provided on a semiconductor substrate; a firstinsulating film with which a surface of the semiconductor substrate iscoated and having an opening to which the pad is exposed; a conductivefilm joined to the pad on a bottom surface of the opening of the firstinsulating film and extending to a surface of the first insulating filmoutside the opening; a second insulating film with which the conductivefilm is coated and having an opening to which a part of the conductivefilm is exposed; and a connecting member arranged so as to be joined tothe conductive film inside the opening of the second insulating film. 2.The semiconductor device according to claim 1 , wherein the connectingmember includes a bump for connection to another solid device.
 3. Thesemiconductor device according to claim 1 , wherein the connectingmember includes another conductive film joined to the conductive film ona bottom surface of the opening of the second insulating film andextending to a surface of the second insulating film outside theopening.
 4. The semiconductor device according to claim 1 , wherein thefirst insulating film includes resin having at least one of an imidebond and an acido bond.
 5. The semiconductor device according to claim 1, wherein the second insulating film includes resin having at least oneof an imide bond and an acido bond.
 6. A process of producing asemiconductor device, comprising the steps of: coating a surface of asemiconductor substrate, provided with a pad for electrical connection,with a first insulating film having an opening to which the pad isexposed; modifying a surface of the first insulating film and an innerwall surface of the opening; forming, by an ion-exchange reaction, athin conductive film with which the surface of the first insulatingfilm, the inner-wall surface of the opening, and a surface of the padexposed on a bottom surface of the opening is coated; thickening thethin conductive film by electroplating with power fed using the thinconductive film; forming a second insulating film with which thethickened conductive film is coated and having an opening to which apart of the conductive film is exposed; and forming a connecting memberjoined to the thickened conductive film inside the opening of the secondinsulating film.
 7. The process according to claim 6 , wherein theconnecting member is a bump for connection to another solid device. 8.The process according to claim 6 , further comprising forming, as theconnecting member, another conductive film joined to the conductive filmon a bottom surface of the opening of the second insulating film andextending to a surface of the second insulating film outside theopening.
 9. The process according to claim 6 , wherein the firstinsulating film includes resin having at least one of an imide bond andan acido bond.
 10. The process according to claim 6 , wherein the secondinsulating film includes resin including at least one of an imide bondand an acido bond.
 11. A process of producing a semiconductor device,comprising the steps of: forming an insulating film on a semiconductorsubstrate; modifying a surface of the insulating film; forming a thinconductive film by an ion-exchange reaction on the modified surface ofthe insulating film; and thickening the thin conductive film byelectroplating with power fed using the thin conductive film.